This invention relates to a load actuating circuit incorporating a semiconductor circuit which actuates an electric load.
In conventional automotive vehicles, semiconductor relays (e.g., power MOSFET) are widely used to actuate various electric loads including a lighting system and a motor driving system. In such a conventional load actuating circuit, a fuse is generally inserted in series with the power MOSFET to prevent the load circuit from being subjected to excessively large current due to short circuit of the wire harness or dead short in the load.
However, recent trends of automotive vehicles are compactness and light weight. Thus, it is preferable to eliminate the fuse for realizing downsizing and weight reduction. To realize this, a load circuit, comprising a load and associated wire harness, needs to be protected against excessive current without using any fuse. For example, a current-detecting resistance may be connected to the power MOSFET which actuates the load. This current-detecting resistance causes a voltage reduction when current flows across the load. Thus, an actual load current value is detected from the voltage reduction caused by the current-detecting resistance. When the load current is increased excessively, the load current is stopped or reduced adequately so as not to exceed a predetermined value (refer to Unexamined Japanese Patent Application No. 8-47168 published in 1996).
However, according to the above-described arrangement, there is a necessity of specially providing the current-detecting resistance. Furthermore, a control circuit is additionally provided to control the power MOSFET in accordance with the detected load current so that the load circuit is protected against excessive current.